1. Field of the Invention
The present invention relates to an overall field requiring spray granulation such as spray dry and melting granulation for preparing, e.g., chemical products, medicines, foods and inorganic powders, and more particularly to a toner for electrophotography.
2. Discussion of the Background
A conventional spray granulation apparatus sprays various materials into a chamber collecting the resultant particles to prepare a particulate, a powdery or a granular product of the materials.
For example, a liquid material formed by dissolving a material in a solvent, dispersing a material in the shape of a slurry therein or melting a material upon application of heat is sprayed in a granulation chamber through a spray nozzle; and the solvent is dried or the melted material is cooled to form solid particles.
A rotation disc nozzle is used to prepare particles having a large particle diameter, e.g., greater than 100 μm, and a two-phase spray nozzle externally mixing is used to prepare particles having a small particle diameter less than 100 μm.
Japanese published unexamined application No. 2005-258394 discloses a method of preparing a toner, wherein after or while a kneaded toner material is melted with a melter, the melted material is sprayed through a high-pressure gas nozzle while discharged in a chamber. Japanese published unexamined application No. 2004-226668 discloses a method of preparing a toner, wherein a dispersion including a finely-dispersed toner material is sprayed with a spray nozzle and solidified while passed through a solidifier to form particles. However, Japanese published unexamined applications Nos. 2005-258394 and 2004-226668 had a problem of clogged nozzle.
Japanese published unexamined application No. 2000-312817 discloses a method of removing a solidified material at the exit of the nozzle with a needle mechanically positioning from the liquid side in order to solve a problem of clogged spray nozzle in a granulation apparatus spraying a liquid material in a granulation chamber therein.
However, when a mechanical cleaner such as a needle is installed in the apparatus, the needle needs to be sealed against the liquid and the nozzle has a complicate structure. First of all, this aims at how to recover a nozzle which is clogged or being clogged and simply a stopgap measure.
Thus, although the spray nozzle is an important element for a spray granulator, the spray nozzle has a large problem of being clogged.
The clogged spray nozzle largely affects controlling particle diameter and particle diameter distribution of the particles produced thereby. When the spray nozzle is clogged, spray conditions of a liquid is disrupted, resulting in generation of coarse particles and a broad particle diameter distribution.
Particularly, a toner is required to have a small particle diameter a particle diameter distribution as sharp as possible. Therefore, generation of coarse particles and a broad particle diameter distribution are fatal problems for preparing a toner by the sprat granulation method.
Because of these reasons, a need exists for a method of preparing a quality toner without clogging the spray nozzle.